1. Field of the Invention
The present invention relates to a thermoplastic polymeric material which predominantly comprises a novel copolymer composed of chain moieties derived from a hard copolymer containing as a comonomer an .alpha.,.beta.-unsaturated dicarboxylic acid anhydride, and polyamide chain moieties, both moieties being chemically bonded to each other, and to a method for the preparation of such thermoplastic polymeric material.
2. Description of the Prior Art
Polystyrene, styrene-acrylonitrile copolymers, acrylonitrile-styrene-butadiene copolymers, polymethyl methacrylate and similar polymeric materials have widely been used as molding materials because of their high dimensional stability and good moldability, while the improvement in their chemicals, thermal and abrasion resisting properties are still desired. On the other hand, polyamides have also been used widely as molding materials because of their superior resistance to chemicals, heat and abrasion. However, polyamides suffer from some disadvantages such as strong shrinkage during molding process which may cause "sink marks" and "warpage" in the molded articles; high hygroscopicity and significant decrease in mechanical strength and large dimensional change after they take up moisture.
It has been proposed that a polyamide is melt blended with polystyrene or a styrene-acrylonitrile copolymer in order to improve the hygroscopicity and other properties of the polyamide (Belgian Patent Nos. 638940 and 638941). However, this technique involves serious disadvantages in that the styrene polymer or copolymer has so poor compatibility with polyamides that the molded articles obtained from such blend show laminar peeling phenomenon and possess inferior mechanical strength. Because of this, such blend is not known as satisfactory molding material. In U.S. Pat. No. 3,966,839 it is disclosed that polystyrene and a polyamide are melt blended with addition of a small amount of a low molecular weight (1000 to 3000 M.W.) styrene-maleic anhydride copolymer which is used in order to improve the compatibility between the polyamide and polystyrene. By the addition of the low molecular weight styrene-maleic anhydride copolymer, an improvement is found in the compatibility between these polymers, but it is still insufficient so that when the blend is used in injection molding into complicated shape the above-mentioned peeling condition may occur, resulting in unfavorable mechanical strength of the molded article.
U.S. Pat. Re. No. 30,322 teaches a polymer obtained by grafting an oligometric polyamide (polymerization degree of 5 to 60) onto an elastomeric trunk polymer. However, when such a polyamide having a low molecular weight is used together with the hard trunk polymer as used in the present invention, the resultant polymer has remarkably low impact resistant strength and rigidity and a low heat distortion temperature so that it cannot provide a polymeric material useful as a thermoplastic molding material.
The reaction of a low molecular weight (ca. 1500 M.W.) styrene-maleic anhydride copolymer with an alkylamine is disclosed in U.S. Pat. Nos. 3,365,399 and 3,444,151. The product of such reaction is a low molecular weight compound and used only as an additive or dispersing agent. There is no prior art which suggests that the above reaction product is used as a molding material. In addition, it is well known that a reaction of a low molecular weight compound is not directly applicable to a homologous high molecular weight compound, because of the low reactivity and the liability to cross-linking reactions of the high molecular weight compound.
In the past many attempts have been proposed which are directed to improving the impact stremgth of polyamides by blending with the polyamide a carboxyl-containing olefin polymer or an olefin-acrylate copolymer. However, in such cases it is believed that the terminal groups of the polyamide and the carboxyl group interact with each other through ionic hydrogen bond rather than cause cross-linking or grafting, as described in British Pat. No. 998,439.
British Pat. No. 1,440,030 describes a blend of a polyamide with a styrene-methacrylate or styrene-acrylate copolymer. However, in this patent any reaction between the polyamide and the styrene copolymer is not noted.
Similarly in our experiments, a combination of a polyamide and a styrene-methacrylic acid or styrene-methyl methacrylate copolymer could not provide a molding material having excellent mechanical strength. Moreover, we found from the results of analytical experiments that the above-mentioned combination did not bring about the formation of a copolymer comprising styrene-methacrylic acid or styrene-methyl methacrylate copolymer chain moieties and polyamide chain moieties bonded to each other.
Accordingly, it is an object of this invention to develop a material having the good performance each of polystyrene and polyamides.